The invention pertains to an electric valve, preferably directly actuated, with a valve member with which an electrical drive unit is associated and which is guided so as to be linearly displaceable relative to a valve housing.
Such valves are widely disseminated in the form of so-called solenoid valves. Their drive unit contains as a rule an electromagnet which drives an armature constituting the valve member. The valve member is guided displaceably in a valve housing, where the valve housing can be formed at least in part by the housing of the electromagnet.
Known electric valves have the disadvantage that the technological barriers to miniaturization are relatively high. Moreover, the operation of solenoid valves is ordinarily associated with relatively high power consumption, which results in the strong generation of heat. Not least of all, electromagnetic drive units reach their limits relatively soon in connection with the realization of high switching speeds. The problem of the present invention is to create a directly actuated, i.e., a non-piloted electric valve of the initially mentioned type that permits smaller overall sizes and higher switching speeds with reduced power consumption.
To solve this problem, the drive unit is implemented as a piezoelectric drive unit which contains at least one piezo-flexural element extending transversely to the displacement direction of the valve member which acts on the valve member at one end and is held stationary with respect to the housing at the other such that its electrically induced flexing motion produces the linear displacement motion of the valve member.
In this way, the flexural behavior of a piezo-flexural element constructed as a piezoconverter is exploited to produce the actuation of a valve member, a direct actuation preferably being provided. This permits previously unattained reductions in the overall size of the valve, it also being possible for the overall length of the valve to be kept very compact because of the transverse arrangement of the existing piezo-flexural element. The piezoelectric drive unit additionally allows high-frequency valve actuation, on the order of, for instance, 200 Hz, so that considerably shorter switching times can be achieved. It is thus possible overall to switch more quickly with better performance data and smaller overall volumes. Furthermore, with a higher efficiency than for solenoid valves, there is lower thermal load.
To be sure, piezo valves, as they are called, are known, for instance, from DE 198 01 613 A1. In these the piezo-flexural element has thus far always been used directly as a valve member and not as a valve drive unit driving a displaceably guided valve member by mechanical coupling.
Advantageous refinements of the invention are derived from the subordinate claims.
The valve member is expediently a valve slide in, for instance, the constructive form of a piston slide valve.
The drive unit of the electric valve may be equipped with only a single piezo-flexural element. If it is motively coupled appropriately to the valve member, then movements of the valve member in the opposite axial direction can also be produced with it, if desired. Additional installation of a restoring unit, such as a spring device opposing the actuation force of the piezo-flexural element, would also be conceivable.
Considered much more advantageous, however, is an embodiment in which the piezoelectric drive device has several piezo-flexural elements acting on the valve member. If these are piezo-flexural elements with identically oriented force action, then elevated actuating forces can be achieved. A constructive form, however, in which two piezo-flexural elements that can act on the valve member with oppositely oriented actuating forces are present is considered particularly expedient. Among other things, a piezoelectrically actuated operating motion of the valve member in both directions can be achieved in this way. Particularly in this context, it is advantageous if a control unit is present that permits a mutually matched electrical triggering of the piezo-flexural elements with variable voltages, in order to achieve different actuation paths or positions as a function of the applied voltage values. For instance, a voltage-gradated triggering of the piezo-flexural elements would be possible here to achieve a multiposition behavior of the valve member. With infinitely variable triggering, on the other hand, a continuous motion behavior and accordingly an electric valve constructed as a continuous valve can be achieved.
It would be possible to position two piezoelements such that they interact with opposing axial end sections of the valve member. Reduced construction expense for design is promised, however, by an embodiment in which two piezo-flexural elements acting on the valve member are arranged adjacent to one another and act on one and the same end section of the valve member.
Especially if the valve member is acted on by two piezoelements with opposite directions of force, it is advantageous if at least one piezoelement, and preferably both, act under an initial mechanical tension on the valve member such that the piezo-flexural elements are deflected at least in part out of their neutral position. This promises a play-free transmission of force onto the valve member by simple means, even in cases in which the piezo-flexural element interacts exclusively by tangential contact with the valve member. Thus switching motions can be implemented with high precision.
In order to be able to integrate the electric valve into an electronic control unit, it is advantageous if a position-detecting device is present, with which at least one position, but preferably every instantaneous position, of the valve member can be determined. Such a position-detection device expediently obtains the necessary information on the basis of the current bending state of at least one piezo-flexural element, which is expediently detected by the use of at least one elongation-measurement strip placed on the piezo-flexural element.
In an advantageous construction, the piezo-flexural elements have an elongated, strip-like support which is coated on at least one side, that is, on one of its two larger surfaces with piezoelectric material, wherein, in particular, a multilayer coating finds use. The individual layer planes could run parallel to the extension plane of the support here; however, an implementation with layer planes oriented transversely to the longitudinal direction of the support, so that the piezoelectric material can be constructed from a strip-like piezo stack, appears particularly advantageous.